  | |
| Observation data EpochJ2000.0 EquinoxJ2000.0 (ICRS) | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 39m 51.36145s[1] |
| Declination | −01° 08′ 34.1135″[1] |
| Apparent magnitude (V) | 3.91[2] |
| Characteristics | |
| Spectral type | K2.5 III[2] |
| B−Vcolor index | 1.32 |
| Variable type | Suspected[3] |
| Astrometry | |
| Radial velocity (Rv) | +24.19±0.36[4] km/s |
| Proper motion (μ) | RA: +46.96[1]mas/yr Dec.: −62.39[1]mas/yr |
| Parallax (π) | 12.39±0.14 mas[1] |
| Distance | 263 ± 3 ly (80.7 ± 0.9 pc) |
| Absolute magnitude (MV) | −0.63[5] |
| Details | |
| Mass | 1.92[2] M☉ |
| Radius | 30±0.04[6] R☉ |
| Luminosity | 241±7[7] L☉ |
| Surface gravity (log g) | 1.78±0.04[7] cgs |
| Temperature | 4,238±22[7] K |
| Metallicity[Fe/H] | −0.06±0.05[7] dex |
| Rotational velocity (v sin i) | 4.5[4] km/s |
| Age | 2.47[2] Gyr |
| Other designations | |
| Ukdah,ι Hya, 35 Hydrae,BD−00°2231,FK5 1250,HD 83618,HIP 47431,HR 3845,SAO 137035.[8] | |
| Database references | |
| SIMBAD | data |
Iota Hydrae (ι Hydrae, abbreviatedIota Hya,ι Hya), formally namedUkdah/ˈʌkdə/,[9] is astar in theconstellation ofHydra, about 8° to the north-northwest ofAlphard (Alpha Hydrae)[10] and just to the south of thecelestial equator.[11] Visible to the naked eye, it is a suspectedvariable star with anapparent visual magnitude that ranges between 3.87 and 3.91.[3] Based upon an annualparallax shift of 12.39 mas measured during theHipparcos mission,[1] it is located around 263 light-years distant.
ι Hydrae (Latinised toIota Hydrae) is the star'sBayer designation.
This star along withTau1 Hydrae,Tau2 Hydrae and33 Hydrae (A Hydrae), were Ptolemy's Καμπή (Kampē); but Kazwini knew them as عقدةʽuqdah (orʽuḳdah) "knot".[12] According to a 1971NASA memorandum,[13]Ukdah was the name of an asterism of four stars: Tau1 Hydrae asUḳdah I, Tau2 Hydrae asUḳdah II, 33 Hydrae asUḳdah III and Iota Hydrae asUḳdah IV. In 2016, the IAU organized aWorking Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN approved the nameUkdah for Iota Hydrae on 1 June 2018 and it is now so included in the List of IAU-approved Star Names.[9]
InChinese,星宿 (Xīng Sù), meaningStar or asterism, refers to anasterism consisting of ι Hydrae,Alphard,τ1 Hydrae,τ2 Hydrae,26 Hydrae,27 Hydrae,HD 82477 andHD 82428.[15] Consequently, ι Hydrae are known as星宿四 (Xīng Sù sì, English:the Fourth Star of Star).[16]
This is anevolvedK-typegiant star with astellar classification of K2.5 III.[2] It is aBarium star, which means that, for a giant star, it displays unusually strongabsorption lines ofsingly-ionizedbarium andstrontium.[17] Iota Hydrae has nearly twice themass of the Sun[2] and has expanded to 30 times theSun's radius.[6] It is around 2.5 billion years old[2] and is spinning with a leisurelyprojected rotational velocity of 4.5 km/s.[4] It may be a member of theWolf 630moving group of stars that share a common trajectory through space.[18]
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